Nothing very obvious there unfortunately...

Do I just have to wait? The disc symbol also stops rotating.
How long did you leave it for before you shut it down? Sometimes Armory can appear to be "frozen" when it is in fact doing something in the background... If it was only a minute or two, then it might be that you were just a bit quick to pull the trigger
However, if you waited like 30-60 minutes and saw no progress then that would be indicative of a serious problem.